The goals of this proposed project are to elucidate the basic biochemical mechanism by which Luteinizing Hormone (LH) regulates steroidogenesis in the corpus luteum and to test the findings in a human system. The basic biochemical studies will be carried out predominantly in an in vitro model system using bovine corpora lutea. These studies are divided into two main objectives: (1) The elucidation of the primary action of LH (i.e. the molecular interaction of LH with its receptor in the corpus luteum cell); (2) The elucidation of the steps subsequent to the primary action of LH, leading to an increase in steroidogenesis. The approach to the first objective is to isolate and purify the adenyl cyclase enzyme system and to determine if the LH receptor is associated with the purified enzyme. The method will involve solubilization and purification using standard enzyme techniques, and the assessment of LH binding. If the receptor is separated from the enzyme activity during the recipitation procedure, it will be purified and characterized separately. The approach to the second objective will involve the purification of the enzyme protein kinase and its effect on the activity of cholesterol esterase and the cholesterol side-chain cleavage enzyme system. Both of the latter systems will be assessed in homogenates and in more purified form. Basic biochemical studies will also be carried out in vivo using the pregnant rat corpus luteum. In these investigations the role of cyclic AMP in the long term maintenance of this hormone will be studied. The findings of the basic biochemical studies carried out in the bovine and rat experiments will be verified using corpora lutea in vitro. In vivo studies are planned to elucidate the mechanism of control of corpus luteum maintenance in the menstrual cycle, pregnancy and postpartum. This will involve the assessment of plasma levels of steroids and gonadotropins, tissue levels of cyclic AMP, prostaglandins and steroids and the binding capacity of the tissues for gonadotropins.